Thermal barrier coatings provide excellent thermal insulation for metal components of gas turbines. Although the relationships between microstructures and mechanical properties as well as thermal conductivity of various TBCs have been extensively studied, there still exists a deficiency of a full understanding on microstructural-related thermal radiation transport inside them, which becomes more and more crucial for advanced gas turbine applications requiring higher operating temperatures. This study aims at presenting a microstructure-based numerical investigation on radiative transfer in the air plasma sprayed (APS) TBC.
In this study, the microstructures of APS TBCs are quantitatively reconstructed based on the Ultra-Small-Angle X-Ray Scattering (USAXS) measurement by the Stony Brook University group, in which the microscale interlamellar pores, intrasplat cracks and globular voids are regarded as oblate spheroids with different sizes and aspect ratios, with a specific distribution of orientations. This is a typical anisotropic medium, in which the physical properties vary with the observing direction. The anisotropic feature of radiative properties including the scattering coefficient and phase function is for the first time demonstrated using the discrete dipole approximation (DDA) method. A modified Monte Carlo method is proposed and implemented to solve the anisotropic radiative transfer problem in such medium. The spectral normal-hemispherical reflectance and transmittance of the coating are thus obtained and further compared with the experimental data from literature as well as our group to validate this numerical method. This work provides a versatile numerical framework for the study of the anisotropic radiative transfer mechanism in APS thermal barrier coatings based on microstructure charaterization.